Large amounts of petrolatum-derived plastics are disposed every year, and serious problems caused by the large amounts of wastes, such as shortage of landfills and environment pollution, have been discussed Under the circumstances, attention has been down by biodegradable plastics, which are degraded by the action of microorganisms in environments, in landfills, or in composts. Biodegradable plastics are under development with the aim of expanding their application to materials for use in the aforementioned environments agriculture, forestry, and fisheries, and also to food containers, packaging materials, sanitary materials, garbage bags, etc., which are difficult to recover/recycle after use.
Particularly, from the viewpoint of carbon dioxide emission reduction or carbon dioxide fixation (carbon neutral), polyhydroxyalkanoates (PHAs), which are plant-derived biodegradable polyesters have been drawing attention. Especially; polylactic acids (PLAs) have been drawing attention because lactic acid, which is the raw material of the polylactic acids, is inexpensive for the reason that it is produced by fermentation using sugars extracted from corn, potato, or the like, and also because the resins are inherently high in rigidity and also high in transparency.
However, such a polylactic acid is problematic in, for example, that it is insufficient in heat resistance because the glass transition temperature thereof is around 55° C. and that the application thereof is limited because it is low in ductility and toughness. In addition, since the crystallization speed of the polylactic acid is slow, it takes a long time for the polylactic acid to be crystallized completely even if it is kept around 100° C., at which its crystallization is most likely to advance. Thus, there is also a problem of poor productivity.
PTL 1 proposes a method of blending a polylactic acid with a resin other than the polylactic acid and a soluble azo lake as a crystal nucleating agent in order to improve heat resistance and processability. However, the biodegradability is not sufficiently high and substantially no high effect has been obtained because a resin other than biodegradable resins is blended.
PTL 2 proposes a method of blending a polylactic acid, a poly-3-hydroxybutyric acid, an inorganic filler, and a crystal nucleating agent in order to obtain a resin material for the low warpage articles being excellent in mechanical performance and biodegradability. However, in order to increase the heat resistance, it is necessary to increase the percentage of the poly-3-hydroxybutyric acid, which leads to a problem that molding issues such as burrs tend to occur.
PTL 3 discloses a biodegradable polyester film made of a polylactic acid and a biodegradable polyester based on an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and an aliphatic dihydroxy compound, and the like. According to the patent literature, a film excellent in tear strength can be obtained, but the film is not satisfactory in heat resistance.